Mechanistic studies on the cobalt(II) Schiff base catalyzed oxidation of olefins by O2

Abstract

determined by the number of localized bonds in a Kekuli? structure. J . Am. Chem. SOC. 1987, 109, 314-379 responds to a set of three localized a-bonds that interact by electron-electron and overlap repulsions. The S C F energy difference between the localized and delocalized C6H6 is then the requested QMRE as shown in 21 in the text.Determination of Overlap Repulsion. The overlap repulsion can Appendix 2. Ab Initio Determination of QMRE This method was developed by K~l l m a r .~* Using benzene as an example, one first performs a standard S C F calculation on benzene to Obtain the SCF energy Of the C6H6 species* In a 'econd the pure KekulC form is generated by replacing the localized a-Mos extracted from a calculation Of ethylene with the Same be estimated from the energy difference between two guess functions, one in which the localized ethylene +bond orbitals are orthonormalized and one in which they are not. The energies of these two guess functions are obtained at the first cycle of the by three C-C bond length as in benzene. The PMOS remain those of benzene. The three localized a-MOs are then orthonormalized SCF calculation. by a unitary transformation which leaves the complete wave function unchanged. The SCF energy of this Kekule form cor- Abstract: The cobalt complex [bis(salicylidene-y-iminopropyl)methylamine]cobalt(II),CoSMDPT, has been shown to catalytically oxidize olefins in the presence of dioxygen or hydrogen peroxide. When terminal olefins are oxidized, the methyl ketone and corresponding secondary alcohol are produced selectively. Internal as well as terminal olefins are oxidized. The most common pathway for the oxidation of olefins catalyzed by first-row transition metals-autoxidation-has been ruled out in this sydem. A Wacker-type mechanism, oxidation by peracids, and mechanisms involving the formation of peroxymetallocycles have also been ruled out. A new mechanism for O2 oxidations is proposed which involves oxidation of the primary alcohol solvent by CoSMDPT to produce the corresponding aldehyde and hydrogen peroxide. Reaction of hydrogen peroxide with CoSMDPT occurs to form a cobalt hydroperoxide, which can be viewed as a stabilized hydroperoxy radical which has spin paired with the dZ2 electron of CoSMDPT. The cobalt hydroperoxide then adds to the olefin double bond, leading to formation of an alkyl hydroperoxide. Haber-Weiss decomposition of this alkyl hydroperoxide by CoSMDPT produces the observed ketone and alcohol products. Deactivation of the catalyst is due to oxidation of the ligand system of the cobalt complex as well as formation of a pperoxo-dicobalt complex.

Synthesis and characterization and antibacterial activity of some new transition metal complexes with ciprofloxacin-imine

“…The Schiff bases complexes have been used in catalytic reactions and as models for biological systems [8,9]. Metal complexes play an essential role in agriculture, pharmaceutical and industrial chemistry [10,11].…”

Autoxidation of Cycloalkenes by the System “Molecular Oxygen-bis(acetylacetonato) Cobalt (II) Complex-butyraldehyde”

“…8,[22][23] For example, in the presence of isobutyraldehyde the epoxidation of cyclohexene catalyzed by bis-2-acetoacetoxy-ethylmethacrylate copper for 24 h affords epoxycyclohexane with 99% selectivity and 84% conversion. 8 On the other hand, epoxidation of alkenes in the presence of cobalt complexes has attracted much less attention, [24][25][26][27][28][29] and the reported studies mainly focus on the oxidation of monoterpenes catalyzed by cobalt halides 24,28 or a silica-supported cobalt complex. 25 In those catalytic systems, the defects of low conversion and selectivity still exists.…”

Electrochemical Reduction of 1-{[(4-Halophenyl)imino]methyl}-2-naphthols in Aprotic Media

“…3 They are also used as model systems for biological macromolecules and catalytic reactions. 4,5 Although these have been numerous studies on 2-hydroxy-1-salicylaldehyde Schiff bases, the studies were made on Schiff bases prepared by using of 2-hydroxy-1-napthaldehyde and its reduction of carbonyl compounds both in aqueous and nonaqueous media. The electrode process, which was involved in the reduction of carbonyl compounds is understood known in substantial detail.…”